A. Overall objectives: 1. To clarify the cellular and molecular bases for regulation of immunoglobulin gene expression 2. To clarify the cellular and molecular bases for B lymphocyte development 3. To identify B cell line models representing different stages of B cell development which can differentiate or dedifferentiate in appropriate in vivo or in vitro microenvironments 4. To clarify the relationships between B lymphocyte transformation and B-lymphocyte development